Can you activate a planeswalker loyalty ability the same turn it enters if it has haste?

Normally, a planeswalker's loyalty abilities cannot be activated the turn it enters the battlefield if it came under your control that turn. This restriction comes from CR 306.5b, which states that a player may activate a loyalty ability only if the planeswalker has been under that player's control since the beginning of their current turn — the same rule that governs summoning sickness for creatures.

Haste (CR 702.10) explicitly overrides this restriction. CR 702.10b states that haste removes the condition requiring the permanent to be controlled since the start of the turn, both for attacking and for activating abilities with the tap or untap symbol — but CR 702.10c further clarifies that haste also removes the loyalty ability timing restriction from CR 306.5b. So a planeswalker with haste may activate its loyalty abilities the turn it enters.

It is important to note that the usual once-per-turn limit on loyalty abilities still applies (CR 606.4): you may only activate one loyalty ability of a given planeswalker per turn, and only on your own turn during a main phase when the stack is empty (CR 306.5b).

Example: You cast Chandra, Torch of Defiance and somehow give her haste (e.g., via Fires of Yavimaya). Even though she just entered the battlefield, you may immediately activate one of her loyalty abilities — say, her +1 to exile the top card — during your main phase on the same turn.